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 With Boiler Axis vertical.

on the saddle, and has a plain hole, the connection with Y being
by key only. There are two nuts z and a upon the saddles, and
the screws b and Y move simultaneously on account of their
union by horizontal shaft at d. When, therefore, the driving
shaft L is rotated in its proper direction, so also are the drills u u
and v v, and a downward feed given to the saddle, as described.
The raising or setting of the saddle involves hand gear, the
capstan t turning the screws through pinion and spur wheel, and
the mitre gear before mentioned: but although the spur wheel is
keyed to its shaft, the worm wheel x is not thus secured, and is
only in gear with the screw Y when damped to the wheel ff-while
the nut a is carried in a socket, and is adjustable by mitre gear
to alter the relative heights of the saddles. Horizontal adjust-
ment is made by turning the capstans gg, each of which moves a
pinion within a rack, and the bolts h h serve as adjustable stops.
The drills themselves are worthy of notice. The upper ones, u tr,
are of the twist shape, but have a conical shoulder at the top,
forming a countersinking bit. The lower drills v v are for counter-
sinking only, and their feed, upward or downward, is obtained by
hand wheels and screws jj. The saddles, somewhat loaded with
all this gear, are coupled to chains passing over pullies kk to
balance-weights behind. In drilling a flue fixed upon the rotating
table, the saddles are raised by hand to approximate height, and
advanced horizontally by the capstans gg; then the stops h h are
set. The strap fork is moved on, the countershaft and the drills
rotated, while the feed wheel at x is clamped in gear. The hole
being drilled to proper depth and countersunk, the feed is un-
clamped and the saddle raised to allow the bottom countersinking
to be done by hand feed // Withdrawing the tools v v, the
dividing wheel B is operated to turn the flue by the amount of-the
rivet pitch, and the next pair of holes drilled as before.

Shells of Locomotive boilers are drilled by machines similar in
general build to that just described. A longer bed is needed,
that the standards a and H niay be advanced or separated by
a tommy-bar applied to pinion and rack. An internal dog-chuck
on the faqe plate grips the shell, and the dividing gear remains
the same* The saddles are materially altered, being similar to
those of the radial drill, Fig, 291, excepting that vertical screws